Microplastics in Surface Waters and Sediments from Guangdong Coastal Areas, South China
, Kaihang Xu 1, Han Gong 1, Kai Huang 2,*, Muting Yan 1,* and Jun Wang 1,2,3,*Round 1
Reviewer 1 Report
Dear Authors,
The problem of determining the concentration of microplastics in the environment is a great challenge. We lack a uniform, standardized method of taking research samples, pretreatment of these samples, and the detection techniques are not uniform. Hence the very different results that different authors receive. It is imperative to establish standardized methods for the determination of microplastics in the various components of the environment as soon as possible. It may be possible to increase the resources of experimental data. Therefore, I am proposing some corrections *.
- *Please describe the Raman spectroscopy and micro-Fourier transformed infrared spectroscopy (μ-FTIR) methods in the methodical part.
- ** Highlight your contribution to the Microplastic risk assessment analysis (as it is not visible to me)
Author Response
Reviewer #1:
*Please describe the Raman spectroscopy and micro-Fourier transformed infrared spectroscopy (μ-FTIR) methods in the methodical part.
Response: Thank you for your suggestion. I have added information about the instrument, please see line 137-142.
* Highlight your contribution to the Microplastic risk assessment analysis (as it is not visible to me)
Response: Thank you for your suggestion. I have added this part, please see line 335.
Reviewer 2 Report
Review: Microplastics in surface waters and sediments from Guang-dong coastal areas, south China
The manuscript is clearly written and reports on the findings of microplastics in surface (coastal) waters and sediment along the Guangdong coastline. As such it is quite acceptable. There are, however a number of issues that should be taken care of. The details follow.
Abstract:
Line 21: “433.3 ot 4166.3 items/kg” – this number suggests far too much precision, especially as the microplastics were found in samples of 1 kg – where would the 0.3 items come from? More seriously though, the range is over one order of magnitude, so something like “430 to 4200” would be more appropriate, just as the numbers for the surface water.
Line 24: “38.18%” – for these numbers the same criticism holds. The suggested precision is unwarranted.
Introduction:
Line 41: “difficult to degrade … because … they contain carbon chains” - is this really the reason for the low degradability?
Line 44: “pervasiveness and persistence in the marine environment” – not only there!
Line 50: “It is estimated” -> “It was estimated” - the article dates from 2017, though why projected data for 2015 are quoted is a small riddle.
Lines 52-55: Microplastics have more often been considered carriers for harmful substances, but what amounts of substances can they carry? Is that really relevant?
Line 58: Split the paragraph at “MPs arise …”
Line 70: “a hotspot of research” – the description that following seems to point to Gangdong as a hotspot of pollution, not of research.
Materials and methods:
Line 114: “to ensure ambient pollution” – I guess “to prevent” is meant.
Line 121-125: “Transfer” and “add” – break in the style of description. Turn the sentences into passive voice.
Line 131: “considered … with uniform shape and color” – why is that so? Is it really essential? And what is a uniform shape?
Line 158: “27.9” – round to “28”
Table 1: Avoid the excessive and unwarranted precision of the numbers!
Table 1: Check the numbers for “North Shore Channel” – exponents are misformed
Lines 190-191: What other causes are possible than human activities?
Line 193: So, the more sewage treatment plants, the higher the pollution?
Line 198: “produces … hydrodynamic models” – that is rather oddly stated. Perhaps: “complex flow patterns”?
Lines 204-206: There is no discernable relation between the concentration in the water and in the sediment, so what does the attribution bring us?
Line 209: what is the definition of the various shapes listed here?
Line 213: see my remarks about exaggerated precision above.
Line 225: “In addition” – in addition to what?
Line 228: “and may be due …” – what is the intention of this part?
Line 252: “identification, which …” – split the sentence
Figure 3: Use the same colours for the same categories (size and shape) in panels A and B. That makes the figure easier to interpret.
Section 3.3: again excessive precision shown.
Section 3.4: The text mentions the following quantities: “polymer risk score”, “pollution load index”, “polymer hazard score”, “toxic fraction of polymer”. Of these, only the “pollution load index” is described in any detail. Please explain the others as well – how does one come to a single number for a mixture of different polymers?
Also, the levels suggest a sort of relation between the hazard score and the pollution load index. That is not an inherent relation. Is it a coincidence?
Figure 4: The circles are intended to show the toxicity via the colour and the pollution load via the size, but there is no visible relation.
Author Response
Reviewer #2:
* Line 21: “433.3 ot 4166.3 items/kg” – this number suggests far too much precision, especially as the microplastics were found in samples of 1 kg – where would the 0.3 items come from? More seriously though, the range is over one order of magnitude, so something like “430 to 4200” would be more appropriate, just as the numbers for the surface water.
Response: Thank you for your question. Because of different population pressure, different level of economic development, different surrounding industrial pollution, and the existence of different point source pollution, the degree of microplastic pollution is different. Abundance of microplastics in the Pearl River has been investigated in the range of 80 to 9597 items kg−1
Reference：
Lin, L., Zuo, L., Peng, J., Cai, L., Fok, L., Yan, Y., L, H. Occurrence and distribution of microplastics in an urban river: A case study in the Pearl River along Guangzhou City, China. Sci. Total Environ. 2018, 644: 375–381, https://doi.org/10.1016/j. scitotenv.2018.06.327
* Line 24: “38.18%” – for these numbers the same criticism holds. The suggested precision is unwarranted.
Response: Thank you for your useful suggestion. I have corrected my mistake, please see line 24.
* Line 41: “difficult to degrade … because … they contain carbon chains” - is this really the reason for the low degradability?
Response: Thank you for your useful suggestion. I have corrected my mistake, please see line 41.
*Line 44: “pervasiveness and persistence in the marine environment” – not only there!
Response: Thank you for your suggestion. I have corrected my mistake, please see line 44.
*Line 50: “It is estimated” -> “It was estimated” - the article dates from 2017, though why projected data for 2015 are quoted is a small riddle.
Response: Thank you for your useful suggestion. I have corrected my mistake, please see line 50-51.
Lines 52-55: Microplastics have more often been considered carriers for harmful substances, but what amounts of substances can they carry? Is that really relevant?
Response: Thank you for your question. Microplastics can adsorb heavy metals, antibiotics, bacteria and persistent organic pollutants, thus promoting the entry of these substances into organisms, improving the bioavailability of pollutants and toxicity to organisms.
Reference：
Trevisan, R., Voy, C., Chen, S., Di, Giulio RT. Nanoplastics Decrease the Toxicity of a Complex PAH Mixture but Impair Mitochondrial Energy Production in Developing Zebrafish. Environ Sci Technol. 2019, 53(14):8405-8415. doi: 10.1021/acs.est.9b02003.
Line 58: Split the paragraph at “MPs arise …”
Response: Thank you for your suggestion. I have corrected my mistake, please see line 58.
Line 70: “a hotspot of research” – the description that following seems to point to Gangdong as a hotspot of pollution, not of research.
Response: Thank you for your useful suggestion. I have used another presentation, please see line 70.
Line 114: “to ensure ambient pollution” – I guess “to prevent” is meant.
Response: Thank you for your suggestion. I have corrected my mistake, please see line 115.
Line 121-125: “Transfer” and “add” – break in the style of description. Turn the sentences into passive voice.
Response: Thank you for your suggestion. I have corrected my mistake, please see line 123-124.
Line 131: “considered … with uniform shape and color” – why is that so? Is it really essential? And what is a uniform shape?
Response: Thank you for your question. Before counting the abundance of microplastics, we should understand and master the morphological characteristics of microplastics. Understanding the shape and color of microplastics can distinguish microplastics from gravel particles. Uniform shape, that is, microplastics are generally regular shape, different from gravel with sharp angles; uniform color is in a microplastics, the color is the same, there is no color loss or uneven color distribution.
Line 158: “27.9” – round to “28”
Response: Thank you for your suggestion. I have corrected my mistake, please see line 166.
Table 1: Avoid the excessive and unwarranted precision of the numbers!
Response: Thank you for your suggestion. I have corrected my mistake.
Table 1: Check the numbers for “North Shore Channel” – exponents are misformed
Response: Thank you for your useful suggestion. I have corrected my mistake, please see Table 1.
Lines 190-191: What other causes are possible than human activities?
Response: Thank you for your question. It is emphasized here that the main source of microplastic pollution in Guangdong coast is human activity. In the discussion of the results, it was also mentioned that human activities are diverse, such as domestic waste, fishing, and agricultural cultivation. There are different point source pollution in different places, the corresponding pollution degree will be different, the hydrodynamic conditions will be different, and the abundance of microplastics will also be different. According to the abundance and composition of microplastics, the main sources of pollution of microplastics were analyzed, which provided the basis for the formulation of environmental system.
Line 193: So, the more sewage treatment plants, the higher the pollution?
Response：Thank you for your question. The entry ways of MPs into the aquatic environment include urban runoff, settling from the air and efflfluent discharge of wastewater treatment plants.
Reference:
Li, X., Chen, L., Mei, Q., Dong, B., Dai, X., Ding, G., Zeng, EY. Microplastics in sewage sludge from the wastewater treatment plants in China. Water Res. 2018, doi: 10.1016/j.watres.2018.05.034.
Zubris, K.A.V., Richards, B.K., 2005. Synthetic fibers as an indicator of land application of sludge. Environ. Pollut. 138 (2), 201-211.
Lv, X., Dong, Q., Zuo, Z., Liu, Y., Huang, X., & Wu, W. M. (2019). Microplastics in a municipal wastewater treatment plant: Fate, dynamic distribution, removal efficiencies, and control strategies. Journal of Cleaner Production, 225, 579-586.
Line 198: “produces … hydrodynamic models” – that is rather oddly stated. Perhaps: “complex flow patterns”?
Response: Thank you for your suggestion. I have corrected my mistake, please see line 208.
Lines 204-206: There is no discernable relation between the concentration in the water and in the sediment, so what does the attribution bring us?
Response：Thank you for your question. It shows that the abundance of microplastics in sediments in this area is affected by many factors.
Line 209: what is the definition of the various shapes listed here?
Response: Thank you for your question. First, figure 2 shows each microplastic morphology. The fiber is linear microplastic, the film is flake microplastic, the particle is block microplastic, and the ball is spherical solid structure.
Line 213: see my remarks about exaggerated precision above.
Response: Thank you for your suggestion. I have corrected my mistake, please see line 224.
Line 225: “In addition” – in addition to what?
Response: Thank you for your question. I have used another presentation, please see line 236.
Line 228: “and may be due …” – what is the intention of this part?
Response: Thank you for your question. Compared with surface water, more debris is found in sediments, which mainly explains the reason why sediment contains more fragments.
Line 252: “identification, which …” – split the sentence
Response: Thank you for your suggestion. I have corrected my mistake, please see line 266.
Figure 3: Use the same colours for the same categories (size and shape) in panels A and B. That makes the figure easier to interpret.
Response: Thank you for your suggestion. I have corrected my mistake, please see Figure 3.
Section 3.3: again excessive precision shown.
Response：Thank you for your suggestion. I have corrected my mistake, please see section 3.3.
Section 3.4: The text mentions the following quantities: “polymer risk score”, “pollution load index”, “polymer hazard score”, “toxic fraction of polymer”. Of these, only the “pollution load index” is described in any detail. Please explain the others as well – how does one come to a single number for a mixture of different polymers?
Response：Thank you for your question. Lithnner et al. obtained the hazard scores of different polymers based on the classification of monomers composed of polymers (polymer hazard score). Polymer hazard score is polymer risk score in this manuscript, I have corrected my mistake in the manuscript.
Also, the levels suggest a sort of relation between the hazard score and the pollution load index. That is not an inherent relation. Is it a coincidence?
Response: Thank you for your question. At present, there is no unified method and standard for the risk assessment of microplastics pollution in water samples and sediments. The classification standard of microplastics pollution risk adopted here refers to the research of Xu et al. The classification of pollution risk categories should be combined with polymer index and pollution load index.
Reference:
Xu, P., Peng, G., Su, L., Gao, Y.Q., Gao, L., Li, D. Microplastic risk assessment in surface waters: A case study in the Changjiang Estuary, China. Mar. Pollut. Bull. 2018, 133, 647-654, https://doi.org/10.1016/j.marpolbul.2018.06.020
Figure 4: The circles are intended to show the toxicity via the colour and the pollution load via the size, but there is no visible relation.
Response：Thank you for your suggestion. The circle size is not different, the PLI is Ⅳ, indicating that although the abundance of microplastics varies from place to place, the PLI is at the same level. But above the color, there is a certain difference in the sampling point. The color represents the polymer toxicity index of the region, the polymer hazard score is different, and the grade of the corresponding polymer risk index will be different.
Reviewer 3 Report
Li et al. survey “Microplastics in surface waters and sediments from Guangdong coastal areas, south China” and additionally classify risk of these microplastics on the basis of abundance and polymer type. Given the intensity of plastic manufacturing, population pressure, and underdeveloped waste management, this is an important area to study risk of microplastic. However, I think the paper needs to be clearer in the presentation of methods and results because meaning is often obscured. In its present state, it is difficult to assess the impact of the paper.
Abstract: What is considered “small” here - <2 mm? Other studies would say that <100 micron is “small”. This is a subjective description, so be exact.
Introduction: There is a previous study of microplastics in this region, so it’d be great to know more about it to know what is “lacking”. Under what conditions were previous data collected? Results: Does combination of the present study with data from previous study offer any additional insight? [Line155]
Methods:
Some additional detail in methods is needed. Write methods in past tense reporting style. Section needs to be edited for sentence flow (e.g. break up long sentences).
- What type of water sampler. A grab sample; what material was the sampler made of?
- Blanks are done to “monitor ambient pollution” not “ensure” (word choice). How much water was used for each blank?
- What magnification was used for stereomicroscopy?
- What was the model of the Raman? What were the conditions of Raman and FTIR acquisition?
Results:
Figures 1 and 3 are difficult to read. There is probably room in Figure 1 to label the bars with the data #MP. Add error bars. Can’t read map labels well. Cannot tell the difference between circle sizes; better perhaps to label them with scores.
What is regenerated cellulose –rayon and viscose is how I interpret this, but “cotton” is mentioned in Line . Is regenerated cellulose synthetic, semi-synthetic, or non-synthetic?
Some explanations are presented which seem to make sense but should have some analysis to support them. For example, L170-178: can you conduct some multiparameter correlation to test for relationship between MP and population, #reported discharge sites, flow velocity, etc in some surrounding radius of sites? L201: What about coastal dilution as a factor? What is the direction of prevailing coastal currents in this region – this can also transport MPs along the coast?
I recommend reducing significant figures in percentages presented (round in tenths or nearest whole number).
Why is ANOVA conducted on the fractions? I believe it’s better to do this just on the count data.
What was the reasoning for the size fractions chosen; those are rather atypical (L237).
Most items were regenerated cellulose, and transparent, but transparent MPs were suggested to be from fishing nets and lines (Line 250): curious, but are fishing nets and lines made of this type of material in the region?
I don’t really understand the risk assessment modeling done; please provide some more description in the methods of the modeling. What is F “pollution degree” – is this “hazard score”? Why was the background value of 0.5 items/cubic meter chosen?
What is hazard score of regenerated cellulose?
225 suspected microplastics were selected for Raman/FTIR: what % of total suspected microplastics counted does this represent? It’s good to mention that “microplastics with high hazard score are likely to be missed” but need this % for context.
Thank you for providing some example spectra in the Supplemental material. But, I did not see an example of “regenerated cellulose”, which was the most common found. How is this differentiated from “cellulose”?
I would suggest evaluating your reporting against recent work aiming to harmonize reporting (e.g. Cowger et al. 2020 DOI: 10.1177/0003702820930292)
Conclusions:
Present your averages in results (L335).
Yellowing of clear/transparent plastics is an indicator of age for polyethylene and polypropylene, but I’m not sure about regen. cellulose and PET: please provide citations regarding “yellow MPs are highly degraded products” (L339) This should really be in results and discussion.
Would be interesting to hear your conclusions regarding the risk and what if anything should be done to reduce the risk. What aquatic life would be most at risk according to the underlying toxicity data? What natural resources near S8 are potentially adversely impacted?
Writing:
Overall the paper could use some additional editing which would improve clarity and ease of reading. Break up long sentences. Avoid repetition (delete passages that repeat information or use the same phrases repetitively; examples: L132-134, L158-161).
Table 1 is missing references.
Author Response
Reviewer #3:
Abstract: What is considered “small” here - <2 mm? Other studies would say that <100 micron is “small”. This is a subjective description, so be exact.
Response: Thank you for your question. My statement is inappropriate and has been corrected in the manuscript, please see line 249-250.
Introduction: There is a previous study of microplastics in this region, so it’d be great to know more about it to know what is “lacking”. Under what conditions were previous data collected?
Response：Thank you for your suggestion. In this study, it is mentioned that there is still a lack of microplastic abundance survey data in many coastal areas of Guangdong. In the investigation of Guangdong coastal microplastics, it mainly focused on small areas of the Pearl River Basin, such as (Hong Kong, Pearl River, South China Sea) or on the abundance of microplastics in water samples and fish samples from Guangdong coastal cities (5 coastal cities). However, there is still a gap in the investigation of the abundance of water samples and sediment microplastics in the coastal area of Guangdong, and the potential point source pollution in each place is unknown to the degree of microplastics pollution in the region. In this study, the abundance data of microplastics in water samples and sediments were investigated in 8 coastal cities, which reflected the potential threat of point source pollution, provided reference for microplastics pollution and provided basis for the formulation of environmental system.
Reference:
Yan, M., Nie, H., Xu, K., He, Y., Hu, Y., Huang, Y., Wang, J. Microplastic abundance, distribution and composition in the Pearl River along Guangzhou city and Pearl River estuary, China. Chemosphere. 2019, 217:879-886. doi: 10.1016/j.chemosphere.2018.11.093.
Lin, L., Zuo, L., Peng, J., Cai, L., Fok, L., Yan, Y., L, H. Occurrence and distribution of microplastics in an urban river: A case study in the Pearl River along Guangzhou City, China. Sci. Total Environ. 2018, 644: 375–381, https://doi.org/10.1016/j. scitotenv.2018.06.327
Fok, L., Cheung, P.K., 2015. Hong Kong at the Pearl River Estuary: a hotspot of microplastic pollution. Mar. Pollut. Bull. 99, 112–118.
Fok, L., Cheung, P.K., Tang, G., Li, W.C., 2016. Size distribution of stranded small plastic debris on the coast of Guangdong, South China. Environ. Pollut. 1–6.
Nie, H., Wang, J., Xu, K., Huang, Y., Yan, M. Microplastic pollution in water and fish samples around Nanxun Reef in Nansha Islands, South China Sea. Sci Total Environ. 2019, 696:134022. doi: 10.1016/j.scitotenv.2019.134022.
Zhang, C., Wang, S., Pan, Z., Sun, D., Xie, S., Zhou, A., Wang, J., Zou, J. Occurrence and distribution of microplastics in commercial fishes from estuarine areas of Guangdong, South China. Chemosphere. 2020, 260:127656. doi: 10.1016/j.chemosphere.2020.127656.
Results: Does combination of the present study with data from previous study offer any additional insight? [Line155]
Response：Thank you for your question. At present, there is no uniform standard for the collection of samples and the separation of microplastics in the world. However, it is necessary to compare the abundance data of microplastics in different regions to reflect the pollution level of microplastics in Guangdong Province. In order to be more comparable, I selected articles investigating the micro-plastic pollution in seawater or the Pearl River Estuary.
Some additional detail in methods is needed. Write methods in past tense reporting style. Section needs to be edited for sentence flow (e.g. break up long sentences).
Response: Thank you for your useful suggestion. I have corrected my mistake.
What type of water sampler. A grab sample; what material was the sampler made of?
Response：Thank you for your question. The water collector is a stainless steel water collector with a capacity of 5 L.
Blanks are done to “monitor ambient pollution” not “ensure” (word choice). How much water was used for each blank?
Response：Thank you for your useful suggestion and question. I have corrected my mistake, please see line 115-116.
What magnification was used for stereomicroscopy?
Response: Thank you for your question. The magnification usually adopted is 60. If we want to identify small size microplastics such as small pellets, we will appropriately increase the magnification of eyepiece, and with the help of tweezers, the suspected particles of microplastics will be poked with tweezers under the microscope for identification.
What was the model of the Raman? What were the conditions of Raman and FTIR acquisition?
Response：Thank you for your question. I have added revelent imformation, please see line 137-142.
Figures 1 and 3 are difficult to read. There is probably room in Figure 1 to label the bars with the data #MP. Add error bars. Can’t read map labels well. Cannot tell the difference between circle sizes; better perhaps to label them with scores.
Response: Thank you for your suggestion. Fig .1: the microplastic abundance represented by columns of a certain length is 2000. This presentation can be seen in multiple studies. Graphs containing error lines added to additional material.
Figure: Actually, Fig .3 the circle size is the same, indicating that the pollution load index of each area in this study is the same, which belongs to the upper middle level. I have changed the diagram. The original intention is to show that different circle sizes represent different pollution load index levels.
Reference：
Yan, M., Nie, H., Xu, K., He, Y., Hu, Y., Huang, Y., Wang, J. Microplastic abundance, distribution and composition in the Pearl River along Guangzhou city and Pearl River estuary, China. Chemosphere. 2019, 217:879-886. doi: 10.1016/j.chemosphere.2018.11.093.
Lin, L., Zuo, L., Peng, J., Cai, L., Fok, L., Yan, Y., L, H. Occurrence and distribution of microplastics in an urban river: A case study in the Pearl River along Guangzhou City, China. Sci. Total Environ. 2018, 644: 375–381, https://doi.org/10.1016/j. scitotenv.2018.06.327
What is regenerated cellulose –rayon and viscose is how I interpret this, but “cotton” is mentioned in Line . Is regenerated cellulose synthetic, semi-synthetic, or non-synthetic?
Response: Thank you for your question. The regenerated cellulose (rayon) in this study is a semi-synthetic material, which has been classified as plastic. Cotton is natural cellulose and does not belong to plastics.
Some explanations are presented which seem to make sense but should have some analysis to support them. For example, L170-178: can you conduct some multiparameter correlation to test for relationship between MP and population, #reported discharge sites, flow velocity, etc in some surrounding radius of sites?
Response: Thank you for your question. The relationship between microplastic pollution and population density has been mentioned in many literatures. Unless it is a closed environment such as a lake (water residence time is longer), large population density will generally cause more serious microplastic pollution.
Reference：
Wang, W., Ndungu, A.W., Li, Z., et al., 2017. Microplastics pollution in inland freshwaters of China: A case study in urban surface waters of Wuhan, China. Sci. Total Environ. 575, 1369-1374.
Mani, T., Hauk, A., Walter, U., et al., 2015. Microplastics profile along the Rhine River. Sci. Rep. 5, 17988.
Fan, Y.J., Zheng, K., Zhu, Z.W., et al., 2019. Distribution, sedimentary record, and
persistence of microplastics in the Pearl River catchment, China. Environ. Pollut. 251, 862-870.
Eriksen, M., Mason, S., Wilson, S., et al., 2013. Microplastic pollution in the surface waters of the Laurentian Great Lakes. Mar. Pollut. Bull. 77 (1-2), 177-182.
L201: What about coastal dilution as a factor? What is the direction of prevailing coastal currents in this region – this can also transport MPs along the coast?
Response: Thank you for your question. Sampling points are distributed along the coast of Guangdong. If it is transported along the coast, perhaps it should not only change the abundance of microplastics in the sediments of these two sampling sites. And this statement is also mentioned in the research of Lin et al.
Reference：
Lin, L., Zuo, L., Peng, J., Cai, L., Fok, L., Yan, Y., L, H. Occurrence and distribution of microplastics in an urban river: A case study in the Pearl River along Guangzhou City, China. Sci. Total Environ. 2018, 644: 375–381, https://doi.org/10.1016/j. scitotenv.2018.06.327
I recommend reducing significant figures in percentages presented (round in tenths or nearest whole number).
Response: Thank you for your suggestion. I have corrected my mistake,
Why is ANOVA conducted on the fractions? I believe it’s better to do this just on the count data.
Response: Thank you for your suggestion. I have corrected my mistake, please see line 227 and 243.
What was the reasoning for the size fractions chosen; those are rather atypical (L237).
Response: Thank you for your question. Microplastics are plastic particles smaller than 5 mm in diameter，and most studies use different sampling methods, the lower limit of MPs detection is 0.3/0.33 mm (eg: Baldwin et al., 2016; Dris et al., 2015; Faure et al., 2015; Fischer et al., 2016; Leslie et al., 2017; McCormick et al., 2014; Su et al., 2016), and microplastics smaller than 0.3 mm are difficult to observe. So for the sake of record and statistics, use this size classification.
Reference:
Baldwin, A.K., Corsi, S.R., Mason, S.A., 2016. Plastic debris in 29 Great Lakes tributaries: relations to watershed attributes and hydrology. Environ. Sci. Technol. 50: 10377–10385. https://doi.org/10.1021/acs.est.6b02917.
Dris, R., Gasperi, J., Rocher, V., Saad, M., Renault, N., Tassin, B., 2015a. Microplastic contamination in an urban area: a case study in Greater Paris. Environ. Chem. 12:592. https://doi.org/10.1071/EN14167.
Faure, F., Demars, C., Wieser, O., Kunz, M., de Alencastro, L.F., 2015. Plastic pollution in Swiss surface waters: nature and concentrations, interaction with pollutants. Environ. Chem. 12:582. https://doi.org/10.1071/EN14218.
Fischer, E.K., Paglialonga, L., Czech, E., Tamminga, M., 2016. Microplastic pollution in lakes and lake shoreline sediments – a case study on Lake Bolsena and Lake Chiusi (central Italy). Environ. Pollut. 213:648–657. https://doi.org/10.1016/j.envpol.2016.03.012.
Leslie, H.A., Brandsma, S.H., van Velzen, M.J.M., Vethaak, A.D., 2017. Microplastics enroute: field measurements in the Dutch river delta and Amsterdam canals, wastewater treatment plants, North Sea sediments and biota. Environ. Int. 101:133–142. https://doi.org/10.1016/j.envint.2017.01.018.
McCormick, A., Hoellein, T.J., Mason, S.A., Schluep, J., Kelly, J.J., 2014. Microplastic is an abundant and distinct microbial habitat in an urban river. Environ. Sci. Technol. 48:11863–11871. https://doi.org/10.1021/es503610r.
Su, L., Xue, Y., Li, L., Yang, D., Kolandhasamy, P., Li, D., Shi, H., 2016. Microplastics in Taihu Lake, China. Environ. Pollut. 216:711–719. https://doi.org/10.1016/j. envpol.2016.06.036.
Most items were regenerated cellulose, and transparent, but transparent MPs were suggested to be from fishing nets and lines (Line 250): curious, but are fishing nets and lines made of this type of material in the region?
Response: Thank you for your question. I made a mistake here and didn't contact the Raman identification results. I have made changes. Bridson et al. observed more colorless fibers in the samples, among which regenerated cellulose (rayon or viscose) accounted for the highest proportion in the identification results of FTIR spectroscopy.
Reference:
Bridson, JH., Patel, M., Lewis, A., Gaw, S., Parker, K. Microplastic contamination in Auckland (New Zealand) beach sediments. Mar Pollut Bull. 2020, 151:110867. doi: 10.1016/j.marpolbul.
I don’t really understand the risk assessment modeling done; please provide some more description in the methods of the modeling. What is F “pollution degree” – is this “hazard score”? Why was the background value of 0.5 items/cubic meter chosen?
Response: Thank you for your suggestion. I have inconsistent statements here, changes have been made in the manuscript. The degree of risk here is the risk category. To determine the risk category of a region, the polymer index and the pollution load index must be combined. background values are determined by reference Xu et al., based on existing studies, which are minimum abundance values. In addition, the background value does not affect the comparison results of formula 2.
What is hazard score of regenerated cellulose?
Response: Thank you for your question. Regenerated cellulose such as rayon has no hazard score and is considered nontoxic
Reference：
Peng, G., Zhu, B., Yang, D., Su, L., Shi, H., Li, D. Microplastics in sediments of the Changjiang estuary, China. Environ. Pollut. 2017, 225, 283-290.
225 suspected microplastics were selected for Raman/FTIR: what % of total suspected microplastics counted does this represent? It’s good to mention that “microplastics with high hazard score are likely to be missed” but need this % for context.
Response: Thank you for your suggestion. I have added a percentage in the manuscript, please see line
Thank you for providing some example spectra in the Supplemental material. But, I did not see an example of “regenerated cellulose”, which was the most common found. How is this differentiated from “cellulose”?
Response: Thank you for your useful suggestion. At present, several studies have found that cellulose accounts for a large proportion of the total samples，and there are many reference to support this result (Wu et al., 2019; Naidoo et al., 2020; Robin et al., 2020). Studies have shown that cellulose-based particles, especially regenerated cellulose (rayon), have been widely reported as microplastics in marine environment (Lusher et al., 2013; Woodall et al., 2014; Yu et al., 2016).
Microplastic contamination includes a wide range of polymers including thermoplastics (e.g. polyethylene and polyamide), thermosets (e.g. polyurethane and epoxy resin) and semi-synthetic materials (e.g. regenerated cellulose and
cellulose acetate) (GESAMP, 2019)
Rayon is a commercial man-made fiber composed of regenerated cellulose, which is a semi-synthetic cellulose fiber made of cellulose derived from wood pulp and carbon disulfide (Comnea-Stancu et al., 2017; Goga et al., 2018), and usually contains dyes or additives known to be harmful to marine life (Remy et al., 2015).
The modified natural polymers, natural rubber and cellulose are further processed into final polymers (rayon and cellophane). Since these polymers have undergone a large number of modifications, they can also be considered artificial and should be included in the definition of plastics (Hartmann et al., 2019).
By identifying the suspected particles of microplastics, it is found that there is a gap between Raman and Fourier Transform Infrared (FTIR) spectroscopy in identifying cellulose and rayon. The former samples were re-identified by FTIR, and it was found that the ratio of rayon to cellulose was 11:2 (78 in total), so most of the cellulose in the experimental samples belonged to regenerated cellulose.
In this study, two instruments were used to identify microplastics. first, Raman identified most of the transparent fibers as cellulose; after that, fourier infrared was used to identify the transparent fibers of another part (72 samples). more than 75% of the samples were identified as rayon, while only 10% of the samples were identified as cellulose. Comnea-Stancu IR et al. mentioned that “When using transmission spectra of fibers and ATR libraries it was not possible to differentiate between man-made and natural fibers. Successful differentiation of natural and man-made cellulosic fibers has been achieved for FT-IR spectra acquired by ATR microscopy and ATR spectroscopy, and application of ATR libraries. As an alternative, chemometric methods such as unsupervised hierarchical cluster analysis, principal component analysis, and partial least squares-discriminant analysis were employed to facilitate identification based on intrinsic relationships of sample spectra and successful discrimination of the fiber type could be achieved.” So Raman has limitations in identifying natural fibers and regenerated fibers. The regenerated cellulose referred to rayon in this study, the artificial filament, I have corrected my mistake.
Reference:
Wu, F.Z., Wang, Y.J., Leung, J.Y.S., Huang, W., Zeng, J.N., Tang, Y.N., Chen, J.F., Shi, A.Q., Yu, X., Xu, X.Q., Zhang, H.G., Cao, L., 2020. Accumulation of microplastics in typical commercial aquatic species: A case study at a productive aquaculture site in China. Sci Total Environ, 708, 135432. http://doi.org/10.1016/j.scitotenv.2019.135432
Naidoo, T., Sershen., Thompson, RC., Rajkaran, A., 2019. Quantification and
characterisation of microplastics ingested by selected juvenile fish species associated with mangroves in KwaZulu-Natal, South Africa. Environ. Pollut. 113635. https://doi.org/10.1016/j.envpol.2019.113635
Robin, R.S., Karthik, R., Purvaja, R., Ganguly, D., Anandavelu, I., Mugilarasan, M., Ramesh, R., 2020. Holistic assessment of microplastics in various coastal environmental matrices, southwest coast of India. Sci. Total Environ. 703, 134947. https://doi.org/10.1016/j.scitotenv.2019.134947.
Lusher, A.L., McHugh, M., Thompson, R.C., 2013. Occurrence of microplastics in the
gastrointestinal tract of pelagic and demersal fish from the English Channel. Mar. Pollut. Bull. 67, 94–99. https://doi.org/10.1016/j.marpolbul.2012.11.028
Woodall, L.C., Sanchez-Vidal, A., Canals, M., Paterson, G.L., Coppock, R., Sleight, V.,
Calafat, A., Rogers, A.D., Narayanaswamy, B.E., Thompson, R.C., 2014. The deep sea is a major sink for microplastic debris. Rot. Soc. Open Sci. 1, 140317. https://doi.org/10.1098/rsos.140317
Yu, X., Peng, J., Wang, J., Wang, K., Bao, S., 2016. Occurrence of microplastics in the
beach sand of the Chinese inner sea: the Bohai Sea. Environ. Pollut. 214, 722–730. https://doi.org/10.1016/j.envpol.2016.04.080
Comnea-Stancu, I.R., Wieland, K., Ramer, G., Schwaighofer, A., Lendl, B., 2017. On the identification of rayon/viscose as a major fraction of microplastics in the marine environment: Discrimination between natural and manmade cellulosic fibers using fourier transform infrared spectroscopy. Applied Spectroscopy 71, 939-950. https://doi.org/10.1177/0003702816660725
Gago, J., Carretero, O., Filgueiras, A., Viñas, L., 2018. Synthetic microfibers in the marine environment: A review on their occurrence in seawater and sediments. Marine Pollution Bulletin 127, 365-376. https://doi.org/10.1016/j.marpolbul.2017.11.070
GESAMP, 2019. Guidelines or the monitoring and assessment of plastic litter and microplastics in the ocean. In: Kershaw, P.J., Turra, A., Galgani, F. (Eds.), Reports and Studies GESAMP (IMO/FAO/UNESCO-IOC/UNIDO/WMO/IAEA/UN/UNEP/UNDP/ISA Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection). GESAMP, pp. 130.
Remy, F., Collard, F., Gilbert, B., Compere, P., Eppe, G., Lepoint, G., 2015. When mi-
croplastic is not plastic: the ingestion of artificial cellulose fibers by macrofauna living in Seagrass Macrophytodetritus. Environ. Sci. Technol. 49, 11158–11166.
https://doi.org/10.1021/acs.est.5b02005
Hartmann, N.B., Hüffer, T., Thompson, R.C., Hassellöv, M., Verschoor, A., Daugaard, A.E., Rist, S., Karlsson, T., Brennholt, N., Cole, M., Herrling, M.P., Hess, M.C., Ivleva, N.P., Lusher, A.L., Wagner, M., 2019. Are we speaking the same language? Recommendations for a definition and categorization framework for plastic debris. Environ. Sci. Technol. 53, 1039–1047. https://doi.org/10.1021/acs.est.8b05297.
Comnea-Stancu IR., Wieland, K., Ramer G, Schwaighofer A, Lendl B. On the Identification of Rayon/Viscose as a Major Fraction of Microplastics in the Marine Environment: Discrimination between Natural and Manmade Cellulosic Fibers Using Fourier Transform Infrared Spectroscopy. Appl Spectrosc. 2017 May;71(5):939-950. doi: 10.1177/0003702816660725. Epub 2016 Sep 20. PMID: 27650982; PMCID: PMC5418941.
I would suggest evaluating your reporting against recent work aiming to harmonize reporting (e.g. Cowger et al. 2020 DOI: 10.1177/0003702820930292)
Response: Thank you for your suggestion. This is a good paper and we has citied it to the manuscript.
Present your averages in results (L335).
Response: Thank you for your suggestion. I have corrected my mistake, please see line 154 and 166.
Yellowing of clear/transparent plastics is an indicator of age for polyethylene and polypropylene, but I’m not sure about regen. cellulose and PET: please provide citations regarding “yellow MPs are highly degraded products” (L339) This should really be in results and discussion.
Response: Thank you for your suggestion. I have corrected my mistake, please see line 260.
Would be interesting to hear your conclusions regarding the risk and what if anything should be done to reduce the risk. What aquatic life would be most at risk according to the underlying toxicity data? What natural resources near S8 are potentially adversely impacted?
Response: Thank you for your question. I have added the conclusions, please see line 337.
Overall the paper could use some additional editing which would improve clarity and ease of reading. Break up long sentences. Avoid repetition (delete passages that repeat information or use the same phrases repetitively; examples: L132-134, L158-161).
Table 1 is missing references.
Response: Thank you for your suggestion. I have corrected my mistake.
